1. Field of the Invention
This invention relates to a photographic processing apparatus and method for processing photographic silver halide photosensitive material (often abbreviated herein as "photosensitive material").
2. Prior Art
Black-and-white photosensitive materials after exposure are processed through a series of steps including black-and-white development, fixation and washing and color photosensitive materials after exposure are processed through a series of steps including color development, desilvering, washing and stabilization. There are used black-and-white developer for black-and-white development, fixer for fixation, color developer for color development, bleaching, blix and fixing solutions for desilvering, city water or deionized water for washing, and stabilizer for stabilization. Photosensitive materials are generally processed by dipping them in the respective solutions which are normally adjusted to a temperature of 20.degree.to 50.degree. C.
Among these steps, the developing step is a step wherein a developing agent which is a reducing agent acts on exposed silver halide grains in the photographic emulsion for reducing Ag.sup.+ into Ag. Silver images are created in this way in black-and-white photography. In the case of color photography, an oxidant of color developing agent reacts with a coupler to form a dye image corresponding to the silver image. The developers experience a lowering of developing power due to deterioration by conversion of the developing agent into an oxidant with the progress of processing and by air oxidation of the developing agent and preservative during quiescent periods.
For avoiding such developer deterioration, a typical prior art approach is to replenish an increased amount of developer. Increased replenishment, however, results in increased usage of chemical agents and water, which is undesirable particularly from the standpoint of environmental protection requiring resource saving and waste liquid reduction. Further, since color developing agents are expensive, their increased consumption is against economy.
More often than not, the developing agents are organic compounds in both black-and-white photography and color photography. Developers containing organic developing agents undesirably cause silver stains with the progress of processing of photosensitive material probably because sulfites used as the preservative form silver sulfite with silver halide dissolved from the photosensitive material. This might be overcome by increasing the replenishment amount, which is undesirable from the standpoint of environmental protection as mentioned above.
As is also well known, metal compounds having reducing ability to exposed silver halide grains are effective for black-and-white developers. Such useful metal compounds include salts and complexes of transition metals such as vanadium, titanium, iron and chromium as disclosed in Journal of Japan Photography, 20 (2), 62 (1957); ibid., 19, 40 (1956), ibid. 29, 31 (1966), Photographic Industry, March, 67 (1976), Journal of the Japanese Chemical Society, No. 9, 1321 (1980), PSE, 19, 283 (1975), Japanese Patent Publication (JP-B) No. 41899/1979, Chiba University Engineering Faculty Technical Report, 14, 1 (1962), ibid., 21 (40), 169 (1970), ibid. 18, 39 (1967), ibid., 21 (39), 11 (1970), Japanese Patent Application Kokai (JP-A) No. 51731/1975, U.S. Pat. No. 3,942,985 and 3,938,978, UKP 1,462,972, JP-A 78534/1982, PSE, 12 (6), 288 (1968 ), and PSE, 14 (6), 391 (1970).
As compared with the organic developing agents, these metal compounds have the advantage that they can be used in acidic or neutral aqueous solutions at higher concentrations without incurring silver stains, but the disadvantage that the developers associated therewith change their oxidation reduction potential with the lapse of time or with the progress of development reaction, failing to maintain a stable activity level. Such a disadvantage can be overcome by increasing the replenishment amount as in the case of organic developing agents at the sacrifice of resource saving and waste liquid reduction.
On the other hand, fixation is to dissolve away the residual silver halide with a suitable dissolving agent for fixing a developed silver image in the case of black-and-white photography. In the case of color photography, silver halide resulting from oxidation of an unnecessary silver image is dissolved away in the bleaching step.
Therefore, the fixer contains a fixing agent which is a silver halide dissolving agent and a preservative. During quiescent periods, the fixing agent and preservative are subject to air oxidation with the lapse of time and on oxidation, they decompose to form sulfides which incur sulfide troubles such as staining of photosensitive material surface. When the fixing agent used is hypo, for example, silver thiosulfate would accumulate in the fixer during processing. Under-fixation or short desilvering would occur unless a fresh fixing solution is replenished in a sufficient amount to reduce the silver thiosulfate concentration in the fixer. In the case of color photography, the above-mentioned troubles due to oxidation are aggravated by entrainment of bleaching solution by photosensitive material.
A typical prior art solution to this problem is to increase the amount of fixer replenished in both black-and-white photography and color photography. Increased replenishment, however, is undesirable from the standpoints of resource saving and waste liquid treatment as previously mentioned.
Under the circumstances, we previously proposed in U.S. Ser. No. 07/730,719 (filed Jul. 16, 1991) or JP-A 273237/1991 a method for treatment of a developer containing an organic developing agent or a fixer by placing it in contact with an electrolyte solution through an anion exchange membrane, immersing a cathode in the developer or fixer and an anode in the electrolyte solution, and conducting electricity between the electrodes. With respect to a developer containing a metal compound as the developing agent, we previously proposed in Japanese Patent Application No. 24137/1991 a similar method of treating the developer by electric conduction.
These methods can treat the developer or fixer in a reducing atmosphere and remove Br.sup.- and other halide ions accumulating during processing by causing them to migrate from the developer or fixer to the electrolyte solution. This can advantageously maintain the development or fixation ability and is thus effective for reducing the replenishment amount.
One problem associated with these methods is that if electric conduction is made in the developer in order to prevent development ability lowering due to air oxidation during quiescent periods, then the developer is removed of Br.sup.- excessively and becomes more likely to fog. When the fixer is treated by the electric conduction method mentioned above, desilvering is short with some types of photosensitive materials, especially black-and-white photosensitive materials and plate-making photosensitive materials such as lithographic photosensitive materials. There is a need for a further reduction in replenishment amount.
In addition, the anion exchange membrane loses its processing ability during an extended period of use, that is, has a short life, especially with color developers containing higher contents of organic developing agents.